1. Field of the Invention
The present invention relates to a delay apparatus which is used in processing of a video signal or the like.
2. Related Background Art
In a video apparatus such as a video camera, VTR, television receiver, or the like, a delay element for delaying a video signal by one horizontal period or a period of time which is 1/2 or an integer times as long as one horizontal period is a significant element to execute processes such as separation, vertical outline correction, skew correction, and the like of chrominance signals. Further, the delay element is also necessary to execute a special effect such as to expand a part of an image pickup signal in a time-dependent manner. In the above video apparatuses, in recent years, the realization of miniaturization, high performance, and low electric power consumption have particularly progressed. Characteristics similar to the above are also demanded for the delay element.
Hitherto, a glass delay line or a CCD (charge coupled device) delay line is mainly used to accomplish the above object. According to the glass delay line, electric/mechanical converting elements are arranged at both ends of the glass and a signal is delayed by using the time which is required for an ultrasonic wave to be propagated in the glass. On the other hand, according to the CCD delay line, a predetermined number of CCDs are driven by predetermined clocks and a signal is delayed by using a transfer time which is required to transfer the signal from one edge of the CCD to the other edge.
In the above delay elements, there is a limitation to further realize the miniaturization high performance, and low electric power consumption for reasons in structure and manufacturing.
For instance, in the case of the glass delay line, the signal of a low frequency cannot be delayed due to the conversion characteristics of the electric/ mechanical converting element or the transfer characteristics of the glass. Therefore, before the signal is input to the delay apparatus, the signal must be certainly modulated at a high frequency and the delayed signal must be demodulated. Thus, modulating and demodulating circuits are necessary. Further, since it is impossible to extremely delay the velocity of a sound wave which is propagated in the glass, there is also a limitation in reducing the length of the glass.
On the other hand, in the case of the CCD delay line, since a transfer driving electrode has a fairly large capacity in principle, a drive pulse consumes a large electric power. In addition, since the amount of charges to be transferred is large, a voltage of about 10V is needed.
Moreover, in order to execute the special effect as mentioned above by the conventional delay element, there is a problem such that a structure and peripheral circuits of such a delay element are very complicated.